JP2003251381A - Nitrogen removal by membrane bioreactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for removing ammonia nitrogen in water by a single tank type nitrification denitrification membrane bioreactor which is effective for purifying organic contaminated water such as waste water or ammonia nitrogen contaminated water. I do. SOLUTION: A porous hollow fiber membrane having a biofilm containing nitrifying bacteria and denitrifying bacteria fixed on an outer surface is used, and a gas containing oxygen is supplied to the inner surface side of the hollow fiber membrane, thereby forming the hollow fiber membrane Nitrogen removal by a membrane bioreactor, characterized in that the raw water is supplied to the outer surface side of the membrane to remove the ammonia component from the raw water by nitrification and denitrification in the biofilm on the porous hollow fiber outer surface Method.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a system for removing ammonia nitrogen in water by a single tank type nitrification denitrification membrane bioreactor, which is effective for purification of organic polluted water such as waste water or ammonia nitrogen polluted water. Regarding

[0002]

2. Description of the Related Art While environmental problems such as eutrophication of the water environment have been pointed out, the importance of wastewater treatment technology containing nitrogen, which is the cause, is increasing. Among them, the biological nitrogen removal technology using microorganisms is drawing attention as a low energy consumption type and highly environmentally compatible technology (Hirata et al., Wat.
Sci. Tech. , 34, 282-289 (199
6)).

Most of the nitrogen in the waste water is organic nitrogen or ammonia nitrogen, and the organic nitrogen becomes ammonia nitrogen in the process of hydrolysis of the organic matter. Therefore,
After all, the removal of nitrogen means the removal of ammonia nitrogen.

Biological nitrogen removal using microorganisms
There are two processes: a process of oxidizing ammonia to nitric acid or nitrous acid (reaction formulas (1) and (2) below) and a process of reducing these oxidation products to nitrogen gas (reaction formulas (3) and (4) below). Consists of processes. The former (the process) reaction is called nitrification, and the latter (the process) reaction is called denitrification. Nitrification is mainly performed by nitrifying bacteria that are aerobic bacteria under aerobic conditions, and denitrification is performed by denitrifying bacteria that are anaerobic bacteria under anaerobic conditions.

[0005] ^{_{<nitrification> 2NH 4 + + 3O 2 →}} 2NO 2 - + 2H 2 O + 4H + (1) 2NO 2 - + O 2 → 2NO 3 - (2)

<Denitrification> 2NO ₃ ⁻ + 2H ⁺ → 2NO ₂ ⁻ + 2OH ⁻ (3) 2NO ₂ ⁻ + 6H ⁺ → N ₂ ↑ + 2H ₂ O + 2OH ⁻ (4)

In the studies so far, these two processes have been carried out in different reactors (reactors) due to the difference in operating conditions (aerobic condition: nitrification, anaerobic condition: denitrification). Et al., Microbiology for Environmental Purification, 137
Page, Kodansha, 1983). However, this method has drawbacks in that the system becomes complicated, the pH needs to be adjusted in each reaction tank (reactor), and the installation area becomes large. Therefore, it has been desired to develop an efficient nitrogen removal reactor capable of removing ammonia from water by sequentially causing both nitrification and denitrification reactions in a single reaction tank.

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a single tank type nitrification denitrification membrane bioreactor which is effective for purification of organic polluted water such as waste water or ammonia nitrogen contaminated water. The purpose is to provide a removal system.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have completed the invention of a nitrogen removal system having the following configurations (1) to (5). Came to do.

(1) A porous hollow fiber membrane having a biofilm containing nitrifying bacteria and denitrifying bacteria fixed on the outer surface thereof is used, and a gas containing oxygen is supplied to the inner surface side of the hollow fiber membrane to form a hollow film. A membrane bioreactor characterized by removing raw water to the outer surface side of the membrane by nitrifying and denitrifying the ammonia component in the raw water in the biofilm on the outer surface of the porous hollow fiber membrane. Nitrogen removal method.

(2) A porous hollow fiber membrane having a biofilm containing nitrifying bacteria and denitrifying bacteria fixed on its outer surface, a means for supplying a gas containing oxygen to the inner surface side of the hollow fiber membrane, Nitrogen for removing and nitrifying and denitrifying the ammonia component in the raw water in the biofilm on the outer surface of the porous hollow fiber membrane, which comprises at least means for supplying raw water to the outer surface side of the hollow fiber membrane. Removal device.

(3) The nitrogen removing apparatus according to (2) above, wherein positively charged groups are fixed on at least the outer surface of the porous hollow fiber membrane.

(4) The inner diameter of the porous hollow fiber membrane is 0.1 mm
The nitrogen removing device as described in (2) or (3) above, which has a thickness of 4 mm or less and a film thickness of 0.05 mm or more and 2 mm or less.

(5) The average pore diameter of the porous hollow fiber membrane is 3 μm
The nitrogen removing device according to any one of (2) to (4) above, characterized in that:

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. In the present invention, a porous hollow fiber membrane having a biofilm containing nitrifying bacteria and denitrifying bacteria fixed on the outer surface is used as a reaction field for nitrification and denitrification. Raw water to be purified (removal of nitrogen) is supplied to the outer surface side where the biofilm is fixed. On the other hand, a gas containing oxygen is supplied and filled on the inner surface side.

The production of a biofilm containing nitrifying bacteria and denitrifying bacteria on the outer surface of the porous hollow fiber membrane is performed, for example, by supplying a gas containing oxygen to the inner surface side of the porous hollow fiber membrane to fill it, By bringing a liquid containing a substrate (ammonia) to which seed sludge has been added into contact with the surface side, it can be formed naturally along with the growth of microorganisms.

The material forming the porous hollow fiber membrane is not particularly limited, but it is advantageous for forming a biofilm that at least the positively charged groups are fixed on the outer surface. It is generally said that nitrifying bacteria have poor adhesion to the surface of the carrier and are unlikely to form a biofilm, but by making the surface positively charged, the adhesion can be improved.

Examples of positively charged groups include quaternary ammonium groups, tertiary amino groups and secondary amino groups. Examples of the method for allowing such positively charged groups to exist on at least the outer surface of the porous hollow fiber membrane include the following methods (1) to (3).

Method Using Porous Hollow Fiber Membrane Formed from Polymer Compound Having Positively Charged Group As described above, non-positively charged membrane materials that are commonly used (polyethylene, polypropylene, polyvinylidene fluoride, polysulfone,
Polyether sulfone, polyacrylonitrile (copolymer of acrylonitrile-containing and other vinyl monomers), cellulose such as cellulose acetate and cellulose derivatives)
A method for coating at least the outer surface of a porous hollow fiber membrane formed from a material with a positively charged charged group A porous hollow fiber membrane formed from a commonly used non-positively charged membrane material (eg, the same as above) Method of introducing positively charged groups to at least the outer surface of the surface by modification reaction such as chemical reaction or graft polymerization reaction

If the pore diameter of the porous hollow fiber membrane is too large, it is difficult to obtain a good biofilm, and if it is too small, oxygen supply from the inner surface side tends to be insufficient. Therefore,
The average pore size is preferably 3 μm or less, and the molecular weight is 1
It is more preferable that the transmittance of ten thousand dextran is 10% or more. The average pore size can be determined by using the method described in ASTM: F316-86 (also known as the half dry method).

The dextran permeability was determined by supplying 0.1% by weight dextran aqueous solution to the inner surface of the hollow fiber membrane at an average filtration pressure of 0.05 MPa, a linear velocity of 1 m / sec, and 25 ° C., and after 40 minutes of filtration. The dextran concentration in the filtered water and the supplied water of is measured with a differential refractometer and calculated from the following formula. Dextran permeability [%] = 100 (dextran concentration in filtered water) / (dextran concentration in feed water)

The dextran having a molecular weight of 10,000 may be used by subjecting dextran synthesized by biosynthesis or the like to a molecular weight fractionation by gel permeation chromatography or the like to extract a fraction having a molecular weight of 10,000. Pharmacia Bio
Dextran T10 commercially available from tech (Uppsala, Sweden) can be used.

The thickness of the porous hollow fiber membrane is not particularly limited, but if it is too thick, it will impede the supply of oxygen from the inner surface side to the biofilm on the outer surface, and if it is too thin, it will be porous hollow fiber. Since it is difficult to maintain the strength of the film, 0.05 mm or more and 2 mm
The following are preferred.

The diameter of the porous hollow fiber membrane is not particularly limited, but the inner diameter is preferably not too small in order to supply and fill a gas containing oxygen with a low pressure loss on the inner surface side. If the outer diameter determined by {(inner diameter) + (twice the film thickness)} is too large, the outer surface area of the membrane that can be filled per unit volume will be small, and the biological membrane area that can be fixed on the outer surface will also be small, which is a disadvantage. is there. Therefore, the inner diameter of the porous hollow fiber membrane is preferably 0.1 mm or more and 4 mm or less.

When a porous hollow fiber membrane having a biofilm on which nitrifying bacteria and denitrifying bacteria are fixed on the outer surface as described above is actually used as a reactor, a plurality of porous hollow fiber membranes are bundled into a container. It can be used in a form called “module” housed inside (eg, supervised and translated by Yoshikawa et al., Membrane Technology, Second Edition, IPC, pp. 397-402, 1997).

The composition and oxygen concentration of the gas containing oxygen supplied to the inner surface of the hollow fiber membrane are not particularly limited, but in the usual case, air can be used.

[0027]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto. [Measurement Method, etc.] (Average Pore Diameter) The average pore diameter of the porous hollow fiber membranes was measured by the half dry method at 25 ° C. using ethanol as the liquid used.
The measurement was performed at a pressure rising rate of 0.01 atm / sec.

(Dextran Permeability) The dextran permeability of the porous hollow fiber membrane was measured using Dextran T10 (Pharmacia Bi) as dextran having a molecular weight of 10,000.
(Otech) and a wet membrane having a length of about 10 cm.

(Porosity) The porosity of the porous hollow fiber membrane was determined by the following formula. Porosity [%] = 100 (wet film weight [g] - dry film weight [g]) / (Density [g / cm ^3] × film volume [cm ^3]) Here, "density" in the above formula Is the density of the pore-wetting liquid, and the “membrane volume” is defined as: membrane volume [cm ³ ] = π {(outer diameter [cm] / 2) ² − (inner diameter [cm] / 2) ² } × (membrane length [Cm]).

(Measurement of water quality of bulk water) Total organic carbon concentration (TOC) and total nitrogen concentration (TN) were measured according to JIS method, respectively, by TOC automatic measuring device (TOC-500 manufactured by Shimadzu Corporation) and ultraviolet absorption. The photometric method (using Hitachi's 150-20 Spectrophotometer) was used.

(Measurement on biofilm) The dissolved oxygen concentration (DO) in the thickness direction in the biofilm is measured by the microelectrode method (NP Revsbech, Limology a).
nd Oceanography, 34 (2), 474
-478 (1989)).

[Example of production of porous hollow fiber membrane] JP-A-3-42
According to the technology disclosed in Japanese Patent No. 025 Publication, 18.5 parts by weight of polyethylene resin powder (Asahi Kasei SH-800 grade), 54.3 parts by weight of dibutyl phthalate (DBP), and 27.2 parts by weight of finely divided silica (R-972 manufactured by Nippon Aerosil Co., Ltd.) Part of the composition is premixed, extruded into a hollow fiber with a 35 mm twin-screw extruder, and then dipped in methylene chloride
After extracting BP and further immersing in a 40% by weight aqueous solution of sodium hydroxide at 60 ° C. to extract finely divided silica, washing with water,
By drying, outer diameter 3 mm, inner diameter 2 mm, average pore diameter 0.3 μm, Dextran T10 transmittance 100
%, And a hollow fiber-like porous membrane made of polyethylene (hereinafter, simply referred to as polyethylene membrane) having a porosity of 70% was obtained.

Next, the method of Tsuneda et al. (J. Chromat
Ogr. A, 689, 211-218 (1995)), a diethylamino group, which is a positively chargeable group, was introduced into the entire polyethylene membrane by a method utilizing a radiation graft polymerization method described below.

The polyethylene film was irradiated with an electron beam at 200 kGy in a nitrogen atmosphere by using an electron beam accelerator (accelerating voltage 1.5 MeV, electron beam current 1 mA), and then methanol containing 40% by volume of glycidyl methacrylate (GMA) at 40 ° C. After being immersed in the solution, it was washed with dimethylformamide and methanol, and 0.5% by weight of GMA of the polyethylene membrane was graft-polymerized on the surface of the membrane pores of the polyethylene membrane. GM introduced into the membrane by graft polymerization by immersing this membrane in a 50% by volume aqueous solution of diethylamine.
Diethylamine was added to the epoxy group derived from A to introduce a diethylamino group, which is a tertiary amino group, into the film. The film obtained by introducing a diethylamino group into the entire film thus obtained is hereinafter referred to as a DEA film.

When the DEA film was immersed in a dilute hydrochloric acid aqueous solution to adsorb the hydrochloric acid to the introduced diethylamino group, the amount of decrease in the hydrochloric acid in the aqueous solution was determined by titration with an alkali.
It was found that 90% of the GMA-derived epoxy groups introduced by graft polymerization undergo an addition reaction with diethylamine to introduce diethylamino groups. In addition, D
The EA membrane has an outer diameter of 3.4 mm, an inner diameter of 2.2 mm, an average pore diameter of 0.3 μm, a Dextran T10 transmittance of 100%,
The porosity was 65%.

[Example] Diameter 25 mm, length 250 mm
The DEA membrane obtained in the porous hollow fiber membrane production example was attached to the tubular container (reaction vessel) of No. 3 by moistening, and a pressure of 0.1 kgf / cm ² was applied to the inner surface side using a pure air cylinder. Then, the outer surface side was filled with an aqueous solution containing a substrate (ammonium sulfate) to which seed sludge was added. When the amount of the substrate in the filled substrate solution is low, a part of the filled substrate solution is extracted,
High concentration substrate solution was added. A biofilm was thus formed on the outer surface of the DEA membrane.

After confirming the formation of a biofilm on the outer surface of the DEA membrane, air was applied to the inner surface of the DEA membrane by using a compressor for 0.1
With the pressure of kgf / cm ² being applied, the raw water in which peptone, meat extract and ammonium sulfate were dissolved at a flow rate of 1 × 10 ⁻⁵ m ³ / day from the lower inlet of the reactor at 30 ° C. (TOC: 4500 g / m 2 ³ , TN: 4000 g /
m ³ , NH ₄ ⁺ —N: 3000 g / m ³ ) was semi-batchly supplied to the outer surface side of the hollow fiber membrane, and the water quality of the outlet liquid (bulk water) was measured at the outlet of the upper part of the reactor. At this time, a part of the reactor outlet liquid was returned to the inlet at the lower part of the reactor by a circulation pump at a flow rate of 2.33 m ³ / day and circulated in the reactor.

Furthermore, the outer surface of the DEA film is formed by using a microelectrode.
Of DO in the thickness direction in the biofilm formed above
The measurement was performed. The outline of the reactor used is shown in FIG. reaction
Total organic carbon concentration at the outlet of the vessel: Change in TOC with time
, Total nitrogen concentration: TN, ammonia nitrogen concentration: NH
_Four ⁺-N and nitric acid, nitrite nitrogen concentration: NOx ^--N sutra
The time change is shown in FIG.

The total organic carbon concentration (TOC) at the reactor outlet remained at 180 g / m ³ or less, and 96% or more of the total organic carbon supplied to the reactor was removed. Regarding nitrogen, the total nitrogen component (TN) at the reactor outlet is 800 g.
/ M ³ or less, and 80% or more of the total nitrogen component (TN) supplied to the reactor was removed. The nitrate produced by nitrification of ammonia, nitrite nitrogen concentration (NOx - ^-N) from that has remained at the reactor outlet at 10 g / m ³ or less, the reactor is effectively nitrification and denitrification using The reaction was carried out and it was shown to work effectively as a nitrogen removal reactor.

The thickness of the biofilm on the outer surface of the DEA film gradually increased with time and was about 1600 μm at the 300th day. The measurement result of DO in the thickness direction in this biofilm is shown in FIG. By supplying air from the inner surface of the hollow fiber membrane,
It is understood that all oxygen in the supplied air is consumed in the biofilm, a DO concentration gradient occurs in the biofilm, and aerobic sites and anaerobic sites exist. From this, it can be seen that there is a site where both nitrifying bacteria and denitrifying bacteria can exist in the biofilm, so that the microorganisms are segregated.
The amount of cells in the bulk water in the reactor outside the biofilm was negligible. From the above, it can be seen that the nitrogen removal system by the membrane bioreactor according to the present invention operates effectively.

[0041]

According to the present invention, there is provided a system for removing ammonia nitrogen in water by a single tank type nitrification denitrification membrane bioreactor, which is effective for purification of organic polluted water such as waste water or ammonia nitrogen polluted water. it can.

[Brief description of drawings]

FIG. 1 is a schematic view of a reactor (membrane bioreactor) used in an example of the present invention.

FIG. 2 is a diagram showing a change with time in a total organic carbon concentration (TOC) at an outlet of a reactor in an example of the present invention.

FIG. 3 is a total nitrogen concentration (TN) at the outlet of the reactor, an ammonia nitrogen concentration (NH ₄ ⁺ -N), and
It is a figure which shows the time-dependent change of nitric acid and nitrite nitrogen concentration (NOx ^- N).

FIG. 4 is a diagram showing the measurement results of DO in the thickness direction in the biofilm on the outer surface of the DEA film in the example of the present invention.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C12M 1/40 C12M 1/40 Z C12N 1/20 C12N 1/20 D (72) Inventor Kazutaka Takami Shizuoka Prefecture 1 Asahi Kasei Co., Ltd. (72) Akira Hirata 3-4-2 Okubo Shinjuku-ku, Tokyo 3-4-1 Okubo Waseda University Faculty of Science and Engineering (72) Satoshi Tsuneda 3-4-1 Okubo Shinjuku-ku, Tokyo Waseda University Faculty of Science and Engineering F-terms (reference) 4B029 AA27 BB02 CC03 CC11 4B065 AA01X AC20 BA22 BC41 CA54 4D003 AA01 AB02 BA02 CA08 DA30 EA15 EA30 EA38 FA06 FA10 4D006 GA41 MC62 MB01 MCX MC62 MC22 MC23 MCX MC21 MC29 MC23 MC22 MC22 MC23 MC22 MC23 MC78 NA64 PB08 PB17 PC67 PC69 4D040 BB07 BB42 BB63 BB82

Claims (5)

[Claims] 1. A hollow hollow fiber membrane having a biofilm containing nitrifying bacteria and denitrifying bacteria fixed on the outer surface thereof, and a gas containing oxygen is supplied to the inner surface side of the hollow fiber membrane to obtain the hollow fiber. Nitrogen in a membrane bioreactor characterized in that by supplying raw water to the outer surface side of the membrane, ammonia components in the raw water are removed by nitrification and denitrification in the biofilm on the outer surface of the porous hollow fiber membrane. Removal method. 2. A porous hollow fiber membrane having a biofilm containing nitrifying bacteria and denitrifying bacteria fixed on the outer surface, a means for supplying a gas containing oxygen to the inner surface side of the hollow fiber membrane, and the hollow. Nitrogen removal for nitrifying and denitrifying the ammonia component in the raw water in the biofilm on the outer surface of the porous hollow fiber membrane, which comprises at least means for supplying raw water to the outer surface side of the fiber membrane apparatus. 3. The nitrogen removing apparatus according to claim 2, wherein a positively charged group is fixed on at least the outer surface of the porous hollow fiber membrane. 4. The nitrogen removing apparatus according to claim 2, wherein the porous hollow fiber membrane has an inner diameter of 0.1 mm or more and 4 mm or less and a film thickness of 0.05 mm or more and 2 mm or less. 5. The nitrogen removing device according to claim 2, wherein the porous hollow fiber membrane has an average pore diameter of 3 μm or less.